Method of detecting a level of liquid in a moving cylindrical body

Abstract

A detection method of a liquid level supplies fluid between a moving cylindrical body such as a parison in a film manufacturing process and an ultrasonic transmitter and receiver or an ultrasonic transmitter-receiver opposite to an outer surface of the cylindrical body to keep acoustic contact between an ultrasonic vibration member and the cylindrical body through the fluid. A level of liquid in the cylindrical body is measured on the basis of whether ultrasonic propagating in the fluid and the liquid in the cylindrical body can be received with a predetermined signal level or not. Since the ultrasonic vibration member is brought into contact with the cylindrical body through the fluid, and the contact state therebetween is kept good, and wear, flaw, deformation, frictional heat or the like is not given to the cylindrical body. Further, even if the surface of the cylindrical body is rugged, good contact can be kept.

I claim: 
     
       1. A method of detecting a level of liquid in a moving parison of a film manufacturing process, comprising disposing a transmitting ultrasonic probe outside of said moving parison formed by cooling a melted resin extruded from a die in the form of cylinder and a receiving ultrasonic probe outside of the moving parison from the opposite side of said transmitting ultrasonic probe without contact between the moving parison and said probes, supplying flowing water along a propagation direction of ultrasonic waves in a space between vibration member of said each proves and an outer surface of the moving parison so as to make acoustic contact between the moving parison and said probes, detecting whether the receiving ultrasonic probe receives ultrasonic waves produced from the transmitting ultrasonic probe passed through the liquid so that detecting whether the liquid in the moving parison exists in the propagation path of ultrasonic waves between the probes or not, and pouring the liquid into the parison through the inside of said die when the level of the liquid in the moving parison is lowered than said propagation path by an amount of the liquid consumed. 
     
     
       2. A method according to claim 1, wherein cooling fluid flows on an outer surface of said moving parison and the acoustic contact between said ultrasonic probe and the moving parison is maintained by said cooling fluid and said water flowing along the propagation direction of ultrasonic. 
     
     
       3. A method of detecting a level of liquid in a moving parison of a film manufacturing process, comprising disposing a ring ultrasonic probe around an outer periphery of said moving parison formed by cooling a melted resin extruded from a die in the form of cylinder, said ring probe having an inner surface in which an ultrasonic transmitter and an ultrasonic receiver opposed each other through the moving parison, supplying fluid in a space between the moving parison and the ring probe in a vertical direction to a propagation direction of ultrasonic waves so as to make acoustic contact between the cylindrical body and said transmitter and receiver, detecting whether the receiver receives ultrasonic waves produced from the transmitter passed through the liquid so that detecting whether the liquid in the moving parison exists in the propagation path of ultrasonic waves between the transmitter and receiver or not, and pouring the liquid into the parison through the inside of said die when the liquid surface of the liquid in the moving parison is lower than said propagation path by an amount of the liquid consumed. 
     
     
       4. A method according to claim 3, wherein the moving cylindrical body is a parison in a film manufacturing process and the fluid serves to cool said parison. 
     
     
       5. A method according to claim 3, wherein said ring ultrasonic probe includes a lower portion having a small inner diameter and a space between said lower portion and the moving cylindrical body is formed narrower, said ultrasonic vibration member being embedded in said lower portion having a small inner diameter. 
     
     
       6. A method of detecting a level of a liquid in a moving parison of a film manufacturing process, comprising disposing a transmitting and receiving ultrasonic probe out of only one wall of said moving parison formed by cooling a melted resin extruded from a die in the form of cylinder without contact between the moving parison and the probe, supplying flowing water along a propagation direction of ultrasonic waves in a space between a vibration member of said probe and an outer surface of the moving parison so as to make acoustic contact between the moving parison and the probe, measuring a time which the probe receives ultrasonic impulse echo produced from the probe itself so that detecting whether the liquid in the moving parison exists in the propagation path of ultrasonic waves or not, and pouring the liquid into the parison through the inside of said die when the level of the liquid in the moving parison is lower than said propagation path by an amount of the liquid consumed.